NOAA/WDS Paleoclimatology - Wiles et al.1998 Spring/Summer Gulf of Alaska Temperature Reconstructions

Eight tree-ring chronologies from coastal sites along the Gulf of Alaska (GOA) are used to develop a 227-year (1762-1988) reconstruction of spring/summer (March-September) coastal land temperatures for the region. This reconstruction explains 35% of the variance in the instrumental temperature data. The tree-ring records and reconstruction reflect the documented 1976 transition from cold to warm conditions in the North Pacific and are consistent with regional temperature compilations. Three of the eight ring-width series, from elevational timberline sites where trees are particularly stressed by temperature, extend back to A.D. 1600 and are used to identify additional occurrences of such transitions. The first principal component (PC) scores of these three longer records are positively correlated with spring (March-May) land and sea surface temperatures for the GOA region and are used to reconstruct land surface temperatures. Decadal-scale fluctuations in the reconstructions show agreement with decade-long changes in the intensity of the Aleutian Low pressure cell over the past century, suggesting that the tree-ring data may provide an index of past circulation changes for the northeast Pacific. Blackman-Tukey spectral analyses of both reconstructions indicate significant power at 7-11 years, with additional peaks at 3 years for the spring/summer reconstruction and 19 years for the longer spring temperature series. The modes of variation at about 3 and 7 years may correspond to those associated with the El Niño-Southern Oscillation bandwidth, whereas the 19-year term may relate to a proposed 20-year cycle of North Pacific circulation. The spring temperature series shows generally increased growth over the past century, coinciding with warmer spring temperatures in south coastal Alaska over this interval. Comparison with the entire spring series suggests that the recent warming exceeds temperature levels of prior centuries, extending back to A.D. 1600.

本研究利用阿拉斯加湾（Gulf of Alaska, GOA）沿岸8个树轮年表（tree-ring chronologies），重建了该区域1762-1988年共227年的春夏季（3-9月）沿岸陆地温度序列。该重建序列可解释器测温度数据中35%的方差。树轮记录与重建结果能够反映北太平洋1976年已被文献记载的冷向暖态转变过程，且与区域温度汇编结果一致。8个轮宽序列中有3个源自海拔林线地带——该地带树木受温度胁迫尤为显著——其序列可追溯至公元1600年，被用于识别此类气候转变的额外发生事件。这3条更长序列的第一主成分（principal component, PC）得分与阿拉斯加湾区域春季（3-5月）陆地及海表温度呈正相关，被用于重建陆地表面温度序列。重建序列的年代际波动与过去一个世纪阿留申低压（Aleutian Low）气压系统强度的年代际变化相吻合，这表明树轮数据可作为东北太平洋过去环流变化的代用指标。对两条重建序列的布莱克曼-图基（Blackman-Tukey）频谱分析显示，其在7-11年尺度上存在显著功率谱峰值；其中春夏季重建序列在3年尺度存在额外峰值，而更长的春季温度序列则在19年尺度出现峰值。3年和7年左右的变化模态或与厄尔尼诺-南方涛动（El Niño-Southern Oscillation, ENSO）特征周期相关，而19年尺度的信号则可能与学界提出的北太平洋环流20年周期有关。春季温度序列显示，过去一个世纪阿拉斯加南部沿岸地区的树木生长整体呈增加趋势，与该时段内阿拉斯加南部沿岸春季温度升高的现象相契合。与完整春季序列的对比表明，此次近期升温幅度超过了公元1600年以来的所有历史温度水平。